The accident happened at around 9:40 a.m. in Yulinzi township of Zhengning County, in the city of Qingyang, the local work safety bureau said in a press release.

It said five people died at the scene, including four children and the bus driver, and 15 others had been confirmed dead by midday.

The authority has blamed overloading for the crash, saying the school bus -- a van with nine seats -- was carrying 64 people, most of whom were children from Little Doctor Kindergarten of Yulinzi township.

It said another 45 people, mostly children, were hospitalized with injuries, including 13 serious cases.

The truck had a license plate from neighboring Shaanxi Province and was carrying coal, it said.